Ovarian cancer is a highly lethal neoplasm due to its ability to form tumor implants on the peritoneal mesothelial surface of the abdominal cavity and bowel serosa. The mechanism by which ovarian cancer cells bind to peritoneal mesothelium most likely involves cell-cell recognition through specific adhesion molecules. In order to study this phenomenon, we have developed methods to isolate normal and malignant ovarian epithelial cells and have used an in vitro adhesion assay to quantitate the binding of these cells to peritoneal mesothelium. We have determined that the CD44 adhesion molecule is partly responsible for ovarian cancer cell binding through recognition of mesothelial-associated hyaluronate, a known ligand for CD44. In addition, we have found that ovarian cancer cells also bind through a CD44-independent mechanism which is not related to known adhesion proteins such as integrins or selectins. The first specific aim of this proposal is to determine the in vivo relevance of CD44 in the process of ovarian cancer cell implantation. By using a well-established nude mouse model, we will determine the effects of interfering with CD44 function (with neutralizing antibody or with soluble CD44 protein) on the implantation of CD44-positive ovarian cancer cells in vivo. We will also use a CD44-negative, implantation- incompetent ovarian cancer cell line to determine the effects of CD44 expression (by transfection) on in vivo implantation. In the second specific aim, the regulation of CD44 expression and function will be investigated in normal and malignant ovarian epithelial cells at the gene level using Southern and Northern analyses, and at the protein level using pulse-chase techniques. The third specific aim is to identify additional adhesion molecules which mediate the CD44-independent binding of ovarian cancer cells to peritoneal mesothelium. By using either ovarian cancer cells or mesothelial cells as immunogens, monoclonal antibodies will be generated and screened for their ability to neutralize binding. These neutralizing antibodies will provide useful tools for identifying potentially novel adhesion molecules expressed by either malignant ovarian epithelium or by peritoneal mesothelial cells. These studies should lead to a better understanding of the role of adhesion molecules in the process of ovarian cancer cell implantation. A complete characterization of these structures may eventually permit the design of adhesion antagonists capable of interfering with or reversing the intraabdominal spread of ovarian cancer.